The invention relates generally to fiber quality measurements for cotton classing and, more particularly, to air flow permeability instrument measurements.
Cotton standards are supported by the United States Department of Agriculture (USDA) through its Agricultural Marketing Service (AMS). Cotton standards, and the corresponding classing of cotton, are of great importance in determining the market value of a particular bale of cotton, as well as determining suitability of a particular bale of cotton from a gin for subsequent processing at a particular mill in view of the products and processes of that mill. AMS is responsible for preparing and maintaining such cotton standards and does so in its Standards Section located in Memphis, Tenn.
In 1923, the United States and nine European countries entered into the Universal Cotton Standards Agreement. From that time, up until approximately 1965, USDA/AMS cotton classing xe2x80x9cmeasurementsxe2x80x9d based on the Universal Standards were made entirely by humans. The human measurements included xe2x80x9cgrade,xe2x80x9d xe2x80x9cextraneous matterxe2x80x9d (such as bark and grass), xe2x80x9cpreparationxe2x80x9d (which relates to smoothness of the sample) and xe2x80x9cstaple lengthxe2x80x9d (long fiber content). Instrument-based cotton classing was introduced in 1965, beginning with micronaire, an air flow permeability measurement, followed in 1980 by High Volume Instruments (HVI), which added measurements of length and strength. HVIs currently measure the fiber qualities of Micronaire, Length, Strength, Color and Trash.
Since approximately 1950, various forms of the xe2x80x9cMicronairexe2x80x9d air flow permeability measurement have been widely used in the classification of cotton. The permeability measurement was originally calibrated in terms of linear density or fineness, with dimensions in the United States of micrograms per inch, with a typical and good value being 4 xcexcg/in (10 xcexcg/cm), and with ranges in value from as low as 2 xcexcg/in (5 xcexcg/cm) to as high as 7 xcexcg/in (18 xcexcg/cm). Most varieties, when xe2x80x9cnormally matured,xe2x80x9d have values in the range of 3 xcexcg/in (7.6 xcexcg/cm) to 5 xcexcg/in (12.7 xcexcg/cm). It was later found that this fineness interpretation was incorrect, since the calibration between permeability and true weight fineness could not be robustly adjusted to fit most cotton types, so the fineness dimensions were dropped. But since the measurement was found to be useful for processing, particularly for xe2x80x9cwastinessxe2x80x9d and for other processing problems, the measurement was standardized and its use grew. Micronaire became the first non-human based measurement to enter the trading of cotton, widely, and was introduced officially into AMS classing in 1965.
In the standardization of this simple measurement, a known (by a precision balance) sample mass is compressed into a known, fixed volume, air is forced through this compressed plug, and the resulting air flow permeability, a ratio of flow rate to pressure differential (usually to the one half power), is calibrated in terms of xe2x80x9cacceptedxe2x80x9d values of micronaire provided by the USDA. Thus the measurement is calibrated on cotton at a fixed bulk density of the plug or, alternatively stated, at a fixed compression volume for the fixed and known mass. Nearly 50 years of experience with this measurement substantiate its usefulness but, equally strongly, its shortcomings. Other apparatus has been offered which provides permeabilities at two compressions of the same sample mass. From these data, additional fiber properties, including Maturity and Fineness, can be inferred, based on calibrations for these fiber qualities. These xe2x80x9cdouble compressionxe2x80x9d testers were manufactured by Shirley Developments, Manchester, England and Spinlab, Knoxville, Tenn., and called the Fineness and Maturity Tester and the Arealometer, respectively. These instruments are not widely used because the calibrations are not sufficiently robust and the results are very operator and sample state sensitive. The Arealometer is no longer manufactured.
Further adding to the difficulties for these measurements, definitions for Maturity and Fineness are not widely agreed. The better or xe2x80x9cmore unbiasedxe2x80x9d of the many definitions in use relate to the fiber cross sectional shape and to the fiber cross sectional area, respectively. Such data can only be produced by image analysis of carefully prepared fiber cross sections that are too slow for commercial use, even with modern image analysis methods.
The better basic definitions referred to above require far more rigorous permeability data; permeabilities at tens of compressions are needed, not two. Prior art apparatus is completely inapplicable for extension to acquire permeability readings from tens of compressions. For clarity, we note that the conventional term xe2x80x9ccompressionxe2x80x9d means, more rigorously, bulk density, mass of fiber per unit volume, grams/cm3.
It is therefore seen to be desirable to provide continuous or nearly continuous measurements of rigorous air flow permeabilities, so that robust and useful measurements of cotton Micronaire, Maturity and Fineness can be inferred. It is further seen to be desirable to enable more rigorous calibrations, in terms of basic cross sectional data.
Embodiments of the invention employ sensors to determine when a predetermined mass of fibers has been delivered to a testing chamber, allowing for automated operation without requiring an operator to guess sample weight. The testing chamber has a movable wall, and an actuator drives the movable wall so as to compress the fiber sample in a substantially continuous manner. A transducer measures the position of the movable wall, and a data processing device acquires gas flow rate through the chamber, pressure difference, and position data at a sampling rate while the wall is moving.